The present invention relates to a data processing apparatus, a data processing method, an information storing medium, and a computer program, and particularly to a data processing apparatus and a data processing method for performing a process of decoding data compressed by, for example, MPEG2 (Motion Pictures Experts Group 2) or the like, and outputting video data based on the decoded data and audio data via a display and a speaker, an information storing medium configured to store data in a format suitable for the processing, and a computer program.
Large-capacity data storage devices such as hard discs, optical discs, flash memories, and the like have spread recently. A system has been provided that is capable of random reproduction of video data stored in these storage devices and interactive reproduction processing such as, for example, selecting, extracting, and reproducing video data desired by a user on the basis of a command.
In a reproducing apparatus using, for example, a DVD (Digital Versatile Disc) or the like, video data is divided and set as data in predetermined units. The reproducing apparatus is configured to perform a process in which a user performs an operation, such as a program search, a jump, or the like as required, and only scenes desired to be viewed are reproduced.
Moving image data to be stored on a storing medium, such as a hard disc, an optical disc, a flash memory, or the like, is generally stored after reducing the amount of data by a coding (compression) process. Also, in many cases, data to be transmitted via a network such as the Internet is transmitted after reducing the amount of data by a coding (compression) process, the coded data is stored on a storing medium on a receiving side, and a decoding (decompression) process is performed at the time of reproduction.
Among the best known methods for video compression processing is MPEG (Motion Pictures Experts Group) compression technology. An MPEG stream generated by MPEG compression is stored on a recording medium, such as a DVD or the like, or stored in IP packets in accordance with IP (Internet Protocol) and then transferred on the Internet, whereby data transfer efficiency and data storage efficiency are improved.
MPEG is a technology for realizing high-quality video compression processing. The compression method of MPEG2, which is currently used most often, is a combination of a Discrete Cosine Transform (DCT) as compression using the correlation within a screen, motion compensation as compression based on the correlation between screens, and Huffman coding as compression based on the correlation between code strings. In MPEG2, for predictive coding using motion compensation, a GOP (Group Of Pictures) structure as a group including a plurality of frames formed by three kinds of elements referred to as an I-picture, a P-picture, and a B-picture is employed.
In reproducing frame data including such a group, decoding processing in units of group data, that is, a GOP, is required. Hence, to perform a process such as a program search, a jump, or the like smoothly using a storing medium storing MPEG compressed video data requires a configuration in which decoding processing in GOP units is taken into consideration.
Compressed data to be recorded on a disc or the like is divided into segment units in consideration of decoding processing in the GOP units, and is then stored. At the time of decoding and reproduction, decoding in segment units is performed, and then a reproduction process is performed.
As a conventional technique disclosed for decoding and reproduction processing of compressed data recorded on a disc or the like, there is, for example, a technique in which address data allowing chapter reproduction is recorded in a moving picture user file defined by an MPEG standard and the data is read to reproduce a chapter, thereby enabling the reading of moving pictures from a predetermined position (see Patent Literature 1, for example). Also, a configuration is proposed in which an ID is given to each certain set of data to enable reproduction (random access) and reverse reproduction from a position desired by a user, and a skip search (see Patent Literature 2, for example). Further, a configuration is proposed in which a decoding process is performed on the basis of coded data, one screen is divided on the basis of the decoded data to display a plurality of images, and one selected image is set in a reproduction enable state, thereby making it possible to quickly go over a list of recorded moving images to facilitate program searching (see Patent Literature 3, for example).
[Patent Literature 1]
                Japanese Patent Laid-open No. Hei 7-236116[Patent Literature 2]        Japanese Patent Laid-open No. Hei 8-273296[Patent Literature 3]        Japanese Patent Laid-open No. Hei 10-145743        
In the case where segmented compressed video data of a plurality of contents is stored on a storing medium such as a DVD, or the like, for example, and content change processing, program search processing, jump processing or the like is performed, index information of a content stored on the disc is read in response to a specifying command received from a user, and a search is made for the specified content. Further, a search is made for a segment where a user-specified frame is present, and then the segment extracted is decoded and reproduced. Thus, there is a problem of a long processing time such as the seek time required for a head to move from a position for reading the index information of the disc to a position where the segment to be read is stored when content change processing, program search processing, jump processing, or the like is performed.
A system has recently been devised that stores multiple-viewpoint image data on a disc and changes the viewpoint freely on the basis of a user specification. For example, a system has been devised in which images of a subject taken from a plurality of viewpoint positions or sight line directions are stored on a storing medium, such as a DVD, a CD, or the like, and when a stored image is displayed on a CRT, a liquid crystal display device, or the like, the user freely moves the viewpoint to a position by operating a controller and observes the image of the subject. In such a system, the long time taken to change images when the user selects and displays different viewpoint images one after another causes a delay between the selection and the displayed images, so that good interactive reproduction is not maintained.
Because video from a plurality of viewpoints is required for video contents, the amount of information to be recorded is increased. It is therefore essential that the video be stored as data compressed by MPEG2 or the like. Thus, while a data decoding process is essential, the interruption of video or audio must be avoided as much as possible when a viewer changes images from a plurality of angles.